Objects
in white (except the phaseless Moon) are outside
ten lunar distances (LD) at the date and time shown,
green objects are inside ten LD, yellow inside
Earth's gravitational sphere of influence (SOI), except the Sun, orange
inside two LD, and red inside one LD of Earth. Viewer location is at Earth's
center with the Sun directly to your back. Passing objects orbit the Sun and their motion is seen relative to
the Earth as it orbits the Sun. Object positions translated from a spherical sky dome to this rectangular chart
are increasingly distorted as they move north or south away from the celestial equator.
"Opposition longitude" (in degrees) is exactly opposite to the direction of the Sun through
Earth's center. Asteroids in this region, near the ecliptic and outside Earth's orbit, are at their brightest
as seen from Earth and thus most likely to be discovered and followed. Objects come and go, showing in the
viewer only while inside ten LD or under active observation (and leave trails only when inside 20 LD).
Viewer frame rate seems smoothest at the "good" speed setting, but your experience may differ.
Single-clicking anywhere on the skychart acts like hitting the [Run] button.
This Asteroid/Comet Connection (A/CC) animated illustration runs in HTML5 using data from
NASA/JPL Horizons (see credits) and the
Bright Star Catalog, with star colors per
Mitchell Charity. We welcome
feedback.

Side note to Web developers: This viewer is
the successor to a mostly complete Flash version (see screen shots
sans controls) created with Flex2 ActionScript. The project was finished by starting over again in HTML5 and
JavaScript, which required far less and far simpler coding. Data gathering and processing for this illustration
is all done with Python.

1. Ten lunar distances: A "lunar distance" (LD) is the average distance between Earth and Moon
(about 384,400 km., the same as 238,855 miles or 9.59 times around Earth's equator). Ten lunar
distances has no special astronomical importance but is a useful arbitrary "bubble" within which to organize
this reporting. An approach by a small Solar-System body begins to become interesting at
less than 2.41 LD from Earth as it encounters our planet's gravitational sphere of influence, or
SOI. (Note that until May
2014 we instead used Earth's "Hill sphere" for this
reporting, indicated by the blue line in this illustration at about 3.9 LD, Earth and Moon not shown to
scale). Earth's gravity can change the orbits of objects passing through its SOI. The Moon has its own SOI,
which changes with distance from Earth but is never much more than 0.18 LD. The "Earth-Moon system" is
generally defined as that region of space within a radius of one lunar distance from Earth, so an object can
pass close to the Moon yet not be described as coming "inside" the E-M system.

2. Data credit: All data on this page derived from orbit solutions comes from the NASA JPL
Solar System Dynamics (SSD) Group through its
Horizons system. All information about optical observations
comes from the IAU Minor Planet Center (MPC) and info
about radar observations comes from JPL SSD. The MPC, NASA, and JPL are not associated with this page or
A/CC, and responsibility for the interpretation of this information and its use here rests entirely with A/CC.
Important note: Approach times presented here as to-the-minute may have unstated uncertainties of a
few minutes, or many minutes or even hours for objects with old or very short observation spans, which is
significant because the Earth moves through its own diameter in about seven minutes. Thus actual encounter
distances may vary, occasionally by as much as ten lunar distances. See JPL's
Close Approach Tables for nominal vs. minimum
possible passage distances and times and for their
note about uncertainties.

4. Skychart further notes: For illustrative purposes, the Sun and Moon are shown way out of
proportion to the background sky, each depicted as five degrees in apparent diameter instead of about a half
degree actual. All asteroids as viewed from Earth are single points of light without an apparent diameter.

5. Skychart known issues:

Please report problems. See
here what the animated skychart should look like. If you are not getting
something similar with JavaScript enabled in an HTML5-capable browser, such as Firefox 3.6.3-plus, please
send a screen shot ([Alt-PrtScr] in Windows to copy to memory, open an image editor such as Windows Paint
(found under Start/All Programs/Accessories), then paste and save as a JPEG).